2007 Vol. 32, No. 5
Display Method:
Coupling between the Uplift of Qinghai-Tibet Plateau and Distribution of Basins of Paleogene-Neogene
2007, 32(5): 583-597.
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Abstract:
Recent effort on comprehensive geological mapping in the Qinghai-Tibet plateau and adjacent regions permits recognition of 92 remnant sedimentary basins filled with the Paleogene-Neogene sediments. The relatively large basins with complete Paleogene-Neogene sequences are seen around the margins and at central part of the plateau. Most of the slip-pull basins are distributed along the major faults in the southern, northern, and eastern margins of the plateau. The marine Paleogene-Neogene successions are limited to the southern Tibet and the Yecheng area of Xinjiang. Both the subabyssal and abyssal sequences are exposed at the Gyangze, Saga, Guoyala and Sangmai areas. The deep-water facies successions outcrop in the west, while the shallow-water facies sequences in the east, indicating the closure of the Neo-Tethys Ocean occurring earlier in the east and then in the west. Tectonic uplift of the Qinghai-Tibet plateau occurred first in its eastern part. During the Late Cretaceous, tectonic uplift of the Plateau occurred in its northeastern part and configuration of the Plateau was characterized by paleo-highs in the northeast and depressions in the west. In Paleocene-Eocene interval, the Tengchun-Bange and Kuyake-Golmud areas experienced local tectonic uplifting; the West Kunlun uplift zone broadened easterly; the Qilian uplift zone broadened southerly; the Sunpa-Ganzi uplift zone shrank easterly. The Oligocene configuration of the Plateau was characterized by mountain chains rising along its margins and sedimentary basins occurring in the central part because of tectonic uplifts of the Gangdise and Himalaya blocks. In the same time, the Kunlun-Arjin-Qilian uplift zones have broadened southerly and northerly. In contrast, the expended uplift zones of the Gangdise, Himalaya, Karakorum, and Kunlun blocks feature the paleogeographic contours of the Qinghai-Tibet Plateau during the Miocene-Pliocene. As a result, the paleogeographic configurations of the Qinghai-Tibet Plateau turned over during the Cretaceous-Pliocene transition, with high contours in the east in the pre-Oligocene switching to the high contours in the west at the end-Pliocene. The uplift of the Qinghai-Tibet Plateau during Cenozoic is episodic and the uplifts of various blocks within the Plateau are different in space and time.
Recent effort on comprehensive geological mapping in the Qinghai-Tibet plateau and adjacent regions permits recognition of 92 remnant sedimentary basins filled with the Paleogene-Neogene sediments. The relatively large basins with complete Paleogene-Neogene sequences are seen around the margins and at central part of the plateau. Most of the slip-pull basins are distributed along the major faults in the southern, northern, and eastern margins of the plateau. The marine Paleogene-Neogene successions are limited to the southern Tibet and the Yecheng area of Xinjiang. Both the subabyssal and abyssal sequences are exposed at the Gyangze, Saga, Guoyala and Sangmai areas. The deep-water facies successions outcrop in the west, while the shallow-water facies sequences in the east, indicating the closure of the Neo-Tethys Ocean occurring earlier in the east and then in the west. Tectonic uplift of the Qinghai-Tibet plateau occurred first in its eastern part. During the Late Cretaceous, tectonic uplift of the Plateau occurred in its northeastern part and configuration of the Plateau was characterized by paleo-highs in the northeast and depressions in the west. In Paleocene-Eocene interval, the Tengchun-Bange and Kuyake-Golmud areas experienced local tectonic uplifting; the West Kunlun uplift zone broadened easterly; the Qilian uplift zone broadened southerly; the Sunpa-Ganzi uplift zone shrank easterly. The Oligocene configuration of the Plateau was characterized by mountain chains rising along its margins and sedimentary basins occurring in the central part because of tectonic uplifts of the Gangdise and Himalaya blocks. In the same time, the Kunlun-Arjin-Qilian uplift zones have broadened southerly and northerly. In contrast, the expended uplift zones of the Gangdise, Himalaya, Karakorum, and Kunlun blocks feature the paleogeographic contours of the Qinghai-Tibet Plateau during the Miocene-Pliocene. As a result, the paleogeographic configurations of the Qinghai-Tibet Plateau turned over during the Cretaceous-Pliocene transition, with high contours in the east in the pre-Oligocene switching to the high contours in the west at the end-Pliocene. The uplift of the Qinghai-Tibet Plateau during Cenozoic is episodic and the uplifts of various blocks within the Plateau are different in space and time.
2007, 32(5): 598-604.
Abstract:
Palygorskite in the late Oligocene sediments at Dongxiang, Linxia, northwestern China was investigated by using X-ray diffraction (XRD) and scanning electron microscopy (SEM) . The results show that authigenic palygorskite occurs in the late Oligocene sediments, and trace amount of detrital palygorskite also can be found in the deposits. The authigenic palygorskite is present as silk-like aggregates with thin and long morphology, replacing the I/S mixed-layers along the plate edges, while the detrital palygorskite shows relatively straight fibers, occurring as a single particle in mixture with other fine-grained clay or covering on the surface of plated clay. Clay mineral assemblages of the lower section, the middle section, and the upper section of the late Oligocene sediments are illite, I/S mixed-layers, and kaolinite, illite and I/S mixed-layers, and illite, I/S mixed-layers, and chlorite, respectively, indicating the climatic evolution from humidity to aridity. The amount of palygorskite increasing from the lower to the upper section of the sediments reflects the similar evolution pattern with clay assemblage. Illite and I/S mixed-layers are ubiquitous throughout the late Oligocene sediments. However, the coexistence of illite, I/S mixed-layers, and kaolinite suggests different provenance of the clay. Palygorskite is a common clay mineral of desert soils and is characteristic of aeolian desert dust in the semi-arid and arid regions, and therefore, the occurrence of detrital palygorskite in the late Oligocene sediments implies the loess sedimentation from ~9 Ma in Linxia basin.
Palygorskite in the late Oligocene sediments at Dongxiang, Linxia, northwestern China was investigated by using X-ray diffraction (XRD) and scanning electron microscopy (SEM) . The results show that authigenic palygorskite occurs in the late Oligocene sediments, and trace amount of detrital palygorskite also can be found in the deposits. The authigenic palygorskite is present as silk-like aggregates with thin and long morphology, replacing the I/S mixed-layers along the plate edges, while the detrital palygorskite shows relatively straight fibers, occurring as a single particle in mixture with other fine-grained clay or covering on the surface of plated clay. Clay mineral assemblages of the lower section, the middle section, and the upper section of the late Oligocene sediments are illite, I/S mixed-layers, and kaolinite, illite and I/S mixed-layers, and illite, I/S mixed-layers, and chlorite, respectively, indicating the climatic evolution from humidity to aridity. The amount of palygorskite increasing from the lower to the upper section of the sediments reflects the similar evolution pattern with clay assemblage. Illite and I/S mixed-layers are ubiquitous throughout the late Oligocene sediments. However, the coexistence of illite, I/S mixed-layers, and kaolinite suggests different provenance of the clay. Palygorskite is a common clay mineral of desert soils and is characteristic of aeolian desert dust in the semi-arid and arid regions, and therefore, the occurrence of detrital palygorskite in the late Oligocene sediments implies the loess sedimentation from ~9 Ma in Linxia basin.
2007, 32(5): 605-614.
Abstract:
This paper displays some new thermochronological data on the tectonic processes of the East Kunlun and its adjacent areas in Mesozoic-Early Cenozoic, which were less investigated before. Three thermal events are revealed by different thermochronological methods. The first thermal event, which was a regional tectonic thermal event and established regional tectonic framework, started-up at about 200 Ma and lasted to the interim of the early-middle Jurassic. Its dynamics can be related to the closure of the Songpan-Ganzi-Bayan Har Triassic turbilite basin and the collision between the Qiangtang block and the Kumlun block. The second thermal event, mainly shows a series of NWW-SEE regional faults activity, occurred at about 130-150 Ma and lasted to about 100 Ma, the end of Early Cretaceous. The dynamics of this thermal event can be correspond to the collision between the Lhasa block and the Eurasia plate alone the Bangong-Nujiang suture zone. The last one happened at about 56-45 Ma, showing a extension-coursed uplift. The thermochronological records match well to the geological records which fragmentaryrily presented in the study area and provide a more certain constraint to the tectonic processes.
This paper displays some new thermochronological data on the tectonic processes of the East Kunlun and its adjacent areas in Mesozoic-Early Cenozoic, which were less investigated before. Three thermal events are revealed by different thermochronological methods. The first thermal event, which was a regional tectonic thermal event and established regional tectonic framework, started-up at about 200 Ma and lasted to the interim of the early-middle Jurassic. Its dynamics can be related to the closure of the Songpan-Ganzi-Bayan Har Triassic turbilite basin and the collision between the Qiangtang block and the Kumlun block. The second thermal event, mainly shows a series of NWW-SEE regional faults activity, occurred at about 130-150 Ma and lasted to about 100 Ma, the end of Early Cretaceous. The dynamics of this thermal event can be correspond to the collision between the Lhasa block and the Eurasia plate alone the Bangong-Nujiang suture zone. The last one happened at about 56-45 Ma, showing a extension-coursed uplift. The thermochronological records match well to the geological records which fragmentaryrily presented in the study area and provide a more certain constraint to the tectonic processes.
2007, 32(5): 615-621.
Abstract:
The apatite fission track (AFT) chronology in both sides of Jiali fault belt shows that the AFT age in the north side of the fault belt is 5.6-11.7 Ma which belongs to Late Miocene; and the age of the south side is obviously younger, because the ages of five out of six samples are between 4.0 Ma and 5.9 Ma, belonging to early Pliocene. During 5.6-11.7 Ma, the uplift rate in the north side of Jiali fault belt is 0.07-0.09 mm/a. Since 5.8 Ma, the average denudation rate is 0.50 mm/a, and the average uplift rate is 1.33 mm/a in the north side. While, the average rate of denudation and uplift is 0.62 mm/a and 1.68 mm/a in the south side of Jiali fault belt since 4.7 Ma. The samples collected from both sides of Jiali fault belt reflect the strong uplift since Pliocene, and the south side uplifts more strongly than the north side.
The apatite fission track (AFT) chronology in both sides of Jiali fault belt shows that the AFT age in the north side of the fault belt is 5.6-11.7 Ma which belongs to Late Miocene; and the age of the south side is obviously younger, because the ages of five out of six samples are between 4.0 Ma and 5.9 Ma, belonging to early Pliocene. During 5.6-11.7 Ma, the uplift rate in the north side of Jiali fault belt is 0.07-0.09 mm/a. Since 5.8 Ma, the average denudation rate is 0.50 mm/a, and the average uplift rate is 1.33 mm/a in the north side. While, the average rate of denudation and uplift is 0.62 mm/a and 1.68 mm/a in the south side of Jiali fault belt since 4.7 Ma. The samples collected from both sides of Jiali fault belt reflect the strong uplift since Pliocene, and the south side uplifts more strongly than the north side.
2007, 32(5): 622-628.
Abstract:
There are 52.2 m deep-low lacustrine facies and littoral-low lacustrine facies sediments developed at the later stage of late Pleistocene distributed on the third terrace of Yarlung Zangbo river, Milin region, southeast Tibet, indicating that there was a large ancient dammed lake in the Milin region at that time. In order to discuss the paleoclimate and paleoenvironment of this area, we measured some magnetic parameters of 259 directed samples collected from the Milin airport section. The results indicated that most of the samples have original magnetic fabric, and their κ1 axis indicated the direction of provenance of the Milin ancient dammed lake changed from south and north directions to west and northeast directions, and then to west direction, i. e. a clockwise changing, the changes probably are related to the change in denudation rate induced by differential uplifting of the studied region. The natural remanent magnetization (NRM) and bulk susceptibility (κ) of Milin section have close relationship with particle size and sedimentary facies, which revealed that there are at least four times obvious fluctuates of paleoclimate during later stage of late Pleistocene. The NRM & κ curves of Milin section correspond to IS1-IS6 and IS8 stages of Greenland GISP2 δ18O ice record and also clearly record the Younger Dryas (YD) event and Heinrich events (H1, H2, H3) , indicating that the climate of Milin region was influence by the global climate system.
There are 52.2 m deep-low lacustrine facies and littoral-low lacustrine facies sediments developed at the later stage of late Pleistocene distributed on the third terrace of Yarlung Zangbo river, Milin region, southeast Tibet, indicating that there was a large ancient dammed lake in the Milin region at that time. In order to discuss the paleoclimate and paleoenvironment of this area, we measured some magnetic parameters of 259 directed samples collected from the Milin airport section. The results indicated that most of the samples have original magnetic fabric, and their κ1 axis indicated the direction of provenance of the Milin ancient dammed lake changed from south and north directions to west and northeast directions, and then to west direction, i. e. a clockwise changing, the changes probably are related to the change in denudation rate induced by differential uplifting of the studied region. The natural remanent magnetization (NRM) and bulk susceptibility (κ) of Milin section have close relationship with particle size and sedimentary facies, which revealed that there are at least four times obvious fluctuates of paleoclimate during later stage of late Pleistocene. The NRM & κ curves of Milin section correspond to IS1-IS6 and IS8 stages of Greenland GISP2 δ18O ice record and also clearly record the Younger Dryas (YD) event and Heinrich events (H1, H2, H3) , indicating that the climate of Milin region was influence by the global climate system.
2007, 32(5): 629-637.
Abstract:
The Cenozoic fluvial redbeds are widely exposed in the Tanggula mountains. Dating these!redbeds can provide very important data for understanding the geological history of the Tibetan plateau. The sporopollen assemblage found from the upper part of the Totohe formation are characterized by the dominace of angiospermous pollen, most of the sporopollens being the common elements of Paleogene. Among the angiospermous pollen, there are plenty of tricolpate and tricolporate pollen grains of various kind, mainly including Quercoidites (especially Q. minutus, Q. microhenrici) , Meliaceoidites, Pokrovskaja, and Tricolporopollenites, etc., and the porate pollen is very low in quantity. There is a small amount of herbaceous pollen, such as Scabiosapollis, Labitricolpites, Randiapollis, and Tubulifloridites, as well as sporadic old pollen in these assemblages, such as Classopollis, Pentapollenites, and Jianghanpollis. The quantity of gymnospermous pollen is not high, and the pteridophyte spore is sporadic in the assemblage. Based on the analysis of the characteristics of the sporopollen assemblages, we conclude that the geological age of the upper part of the Totohe Formation is middle and late Eocene, which can provide new basis for further improvement of the Cenozoic stratigraphic system in the Tanggula mountains, northern Tibet.
The Cenozoic fluvial redbeds are widely exposed in the Tanggula mountains. Dating these!redbeds can provide very important data for understanding the geological history of the Tibetan plateau. The sporopollen assemblage found from the upper part of the Totohe formation are characterized by the dominace of angiospermous pollen, most of the sporopollens being the common elements of Paleogene. Among the angiospermous pollen, there are plenty of tricolpate and tricolporate pollen grains of various kind, mainly including Quercoidites (especially Q. minutus, Q. microhenrici) , Meliaceoidites, Pokrovskaja, and Tricolporopollenites, etc., and the porate pollen is very low in quantity. There is a small amount of herbaceous pollen, such as Scabiosapollis, Labitricolpites, Randiapollis, and Tubulifloridites, as well as sporadic old pollen in these assemblages, such as Classopollis, Pentapollenites, and Jianghanpollis. The quantity of gymnospermous pollen is not high, and the pteridophyte spore is sporadic in the assemblage. Based on the analysis of the characteristics of the sporopollen assemblages, we conclude that the geological age of the upper part of the Totohe Formation is middle and late Eocene, which can provide new basis for further improvement of the Cenozoic stratigraphic system in the Tanggula mountains, northern Tibet.
Triassic Palynological Assemblage of the Gulangdi Formation in Tongren County,Qinghai Province,China
2007, 32(5): 638-650.
Abstract:
The Triassic Gulangdi formation is well developed in Gulangdi section, Tongren County, Qinghai Province, western China. 17 Palynological samples were collected from the Section; of these, 6 samples are productive. In total, 30 Palynological genera and 41 species have been identified. Based on the stratigraphic distribution, 2 palynological assemblages can be defined in ascending order: Dictyophyllidites-Di-saccus Assemblage and Verrucosisporites-Di-saccus Assemblage. In the two palynological assemblages, the dominant sporopollens are Dictyophyllidites, Cyathidites, Verrucosisporites and Chasmatosporites, Protopicea, Pinuspollenites. Among them, Dictyophyllidites is quite common from late Triassic to early Jurassic in Eurasia, North America, Oceania. Aratrisporites flourished in middle Triassic in southern hemisphere; in Australia, Asseretospora ranged form middle Triassic to early Jurassic.As we know, a late Triassic ammonite fossil Protrachyceras and bivalve fossil Eumorphotis (Asoella) cf.illyrica had been established from the Gulangdi formation at Huangnan County. Based on the above-mentioned ammonite assemblage and the palynological assemblages proposed in this paper, the Gulangdi formation at Gulangdi section may be assigned to middle-late Triassic in age. Furthermore, the palaeoflora in this region may be growing of the environment from warm temperate zone to subtorrid zone.
The Triassic Gulangdi formation is well developed in Gulangdi section, Tongren County, Qinghai Province, western China. 17 Palynological samples were collected from the Section; of these, 6 samples are productive. In total, 30 Palynological genera and 41 species have been identified. Based on the stratigraphic distribution, 2 palynological assemblages can be defined in ascending order: Dictyophyllidites-Di-saccus Assemblage and Verrucosisporites-Di-saccus Assemblage. In the two palynological assemblages, the dominant sporopollens are Dictyophyllidites, Cyathidites, Verrucosisporites and Chasmatosporites, Protopicea, Pinuspollenites. Among them, Dictyophyllidites is quite common from late Triassic to early Jurassic in Eurasia, North America, Oceania. Aratrisporites flourished in middle Triassic in southern hemisphere; in Australia, Asseretospora ranged form middle Triassic to early Jurassic.As we know, a late Triassic ammonite fossil Protrachyceras and bivalve fossil Eumorphotis (Asoella) cf.illyrica had been established from the Gulangdi formation at Huangnan County. Based on the above-mentioned ammonite assemblage and the palynological assemblages proposed in this paper, the Gulangdi formation at Gulangdi section may be assigned to middle-late Triassic in age. Furthermore, the palaeoflora in this region may be growing of the environment from warm temperate zone to subtorrid zone.
2007, 32(5): 651-661.
Abstract:
Studies on the formation times, resources and tectonic environment of the Cenozoic volcanic rocks in the northern Qiantang area, Qinghai-Tibetan Plateau, formed mostly in Plaeogene, show that these rocks have presented characteristics of typical adakite, according to major and trace elements data tested by many dating and geochemical methods. Of the 12 typical adakite samples in important area, SiO2≥56%(59. 05%-67. 80%), Al2O3≥15%(15.43%-16.63%), MgO < 3% (0. 47%-2. 98%, 1 sample is 3.21%), Mg#>20(21.2-56.5), Na2O/K2O>1(1.03-1.76), Sr>400 × 10-6 (609. 6 × 10-6-3 008. 0× 10-6), Y≤18 × 10-6 (4. 53 × 10-6-13.76 × 10-6), Yb≤1. 9 × 10-6 (0.44 × 10-6-1.35 × 10-6), Sr/Y≥ 40(44. 3-314. 68), La/Yb≥20(20. 11-69. 26), δSr positive anomaly(1.02-7.66, 3 samples are 0. 82, 0. 93, 0. 97), δEu positive anomaly or weak anomaly(0. 77-1.36), LREE enrichment, HREE depletion, HFSEs (Nb, Ta, Ti) strong depletion, 87Sr/86Sr>0. 704(0. 707 101-0. 707 923), 143Nd/144Nd < 0. 512 6(0. 512 382-0. 512 448), 40K-40Ar, 40Ar-39Ar ages are 28. 2-32.2 Ma, 38. 1-46. 8 Ma. The above geochemical features of adakite indicate a primitive magmatic generation process responsible for the partial melting of lower thickened crust of northern Qinghai-Tibetan Plateau and perhaps also represent the process in which the remains in lower crust-up mantle melted and erupted in surface after the subduction of ocean crust in the plateau evolvement during early period.
Studies on the formation times, resources and tectonic environment of the Cenozoic volcanic rocks in the northern Qiantang area, Qinghai-Tibetan Plateau, formed mostly in Plaeogene, show that these rocks have presented characteristics of typical adakite, according to major and trace elements data tested by many dating and geochemical methods. Of the 12 typical adakite samples in important area, SiO2≥56%(59. 05%-67. 80%), Al2O3≥15%(15.43%-16.63%), MgO < 3% (0. 47%-2. 98%, 1 sample is 3.21%), Mg#>20(21.2-56.5), Na2O/K2O>1(1.03-1.76), Sr>400 × 10-6 (609. 6 × 10-6-3 008. 0× 10-6), Y≤18 × 10-6 (4. 53 × 10-6-13.76 × 10-6), Yb≤1. 9 × 10-6 (0.44 × 10-6-1.35 × 10-6), Sr/Y≥ 40(44. 3-314. 68), La/Yb≥20(20. 11-69. 26), δSr positive anomaly(1.02-7.66, 3 samples are 0. 82, 0. 93, 0. 97), δEu positive anomaly or weak anomaly(0. 77-1.36), LREE enrichment, HREE depletion, HFSEs (Nb, Ta, Ti) strong depletion, 87Sr/86Sr>0. 704(0. 707 101-0. 707 923), 143Nd/144Nd < 0. 512 6(0. 512 382-0. 512 448), 40K-40Ar, 40Ar-39Ar ages are 28. 2-32.2 Ma, 38. 1-46. 8 Ma. The above geochemical features of adakite indicate a primitive magmatic generation process responsible for the partial melting of lower thickened crust of northern Qinghai-Tibetan Plateau and perhaps also represent the process in which the remains in lower crust-up mantle melted and erupted in surface after the subduction of ocean crust in the plateau evolvement during early period.
2007, 32(5): 662-670.
Abstract:
The South Altyn marginal fault, northwest Altyn border fault and Hongliugou-Lapeiquan fault in the northern edge of Altyn belong to different fault systems. The south marginal fault was formed in Proterozoic. In mid-late Paleozoic, it was a great intracontinental transform fault of right-lateral slip, and in Mesozoic and Neozoic it was revived in different parts. The northwest fault was formed later. Intense left-lateral slip occurred in Mesozoic-Neozoic and it belongs to the Asian slump fault system. Hongliugou-Lapeiquan fault zone belongs to the central tectonic system of Tarim block. It is an ophiolite complex belt and in early Palaeozoic it was the rift of continental or intercontinental margin. The three faults are different in the evolution history, movement form and tectonic significance, but they are interrelated and affect each other strongly. It is very important to study their tectonic attributions systematically for understanding the west tectonic framework of our country.
The South Altyn marginal fault, northwest Altyn border fault and Hongliugou-Lapeiquan fault in the northern edge of Altyn belong to different fault systems. The south marginal fault was formed in Proterozoic. In mid-late Paleozoic, it was a great intracontinental transform fault of right-lateral slip, and in Mesozoic and Neozoic it was revived in different parts. The northwest fault was formed later. Intense left-lateral slip occurred in Mesozoic-Neozoic and it belongs to the Asian slump fault system. Hongliugou-Lapeiquan fault zone belongs to the central tectonic system of Tarim block. It is an ophiolite complex belt and in early Palaeozoic it was the rift of continental or intercontinental margin. The three faults are different in the evolution history, movement form and tectonic significance, but they are interrelated and affect each other strongly. It is very important to study their tectonic attributions systematically for understanding the west tectonic framework of our country.
2007, 32(5): 671-680.
Abstract:
To establish the list of tectonic-metamorphic events in West Kunlun, we have dated tectonic metamorphic minerals such as amphibole, biotite and didrimit through 40Ar-39Ar isotopic analysis. We have gained several ages that occur many times. Combined with the emplacement age of dikes developed in this area earlier, the 440 Ma and (403±6) Ma 40Ar∕39Ar age of individual mineral biotite in gneiss can represent early Paleozoic underthrut curdle age and the period of accretional process; 382 Ma-284 Ma age of individual mineral biotite in schiefer gneiss and individual mineral amphibole in amphibolite-schist can represent the changing environment from extrusion to spread of this area in early Paleozoic era; 178 Ma-165 Ma 40Ar∕39Ar age of biotite in fragile fault can represent the spurt action of fault tectonic in the background of extrusion strike-slip tectonic and its duration.
To establish the list of tectonic-metamorphic events in West Kunlun, we have dated tectonic metamorphic minerals such as amphibole, biotite and didrimit through 40Ar-39Ar isotopic analysis. We have gained several ages that occur many times. Combined with the emplacement age of dikes developed in this area earlier, the 440 Ma and (403±6) Ma 40Ar∕39Ar age of individual mineral biotite in gneiss can represent early Paleozoic underthrut curdle age and the period of accretional process; 382 Ma-284 Ma age of individual mineral biotite in schiefer gneiss and individual mineral amphibole in amphibolite-schist can represent the changing environment from extrusion to spread of this area in early Paleozoic era; 178 Ma-165 Ma 40Ar∕39Ar age of biotite in fragile fault can represent the spurt action of fault tectonic in the background of extrusion strike-slip tectonic and its duration.
2007, 32(5): 681-690.
Abstract:
The study area is located in the copulae of Qinling-Qilian-Kunlun and adjacent area. In Permian, with the borderline of tectonic-stratigraphic belt in South Qilian, the south is marine facies sediment environment and the north is continental facies sediment environment: In the middle Qilian, North Qilian and Alashan of north district, the sediment is conglomerate, sandstone and mudstone, and it belong to fluvial and lacustrine facies sediment environment; In the south Qilian of mid-district, the sediment environment is belong to marine continental alternation facies with clastic rocks and limestone; In the West Qinling and East Kunlun of the south district, the sediment environment is archipelagic ocean including turbidite rocks of bathyal facies and abyssal facies, basalt, seamount carbonate and so on. During the geological mapping of 1∶250 000 Linxia city and Dingxi City, we found small ocean basin and carbonate seamount formation of early and middle Permian between West Qinling in Ganjia, Xiahe County, Gansu Province. And this can contrast with the archipelagic ocean sediment formation between Qinling and Kunlun in the area of Buqingshan-Huashixia-Xinghai. In late Permian, the sediment is still turbidite rocks of half-sea and deep-sea between Qinling and Qilian, but it is foreland-molasses sediment formation between Qinling and Kunlun.
The study area is located in the copulae of Qinling-Qilian-Kunlun and adjacent area. In Permian, with the borderline of tectonic-stratigraphic belt in South Qilian, the south is marine facies sediment environment and the north is continental facies sediment environment: In the middle Qilian, North Qilian and Alashan of north district, the sediment is conglomerate, sandstone and mudstone, and it belong to fluvial and lacustrine facies sediment environment; In the south Qilian of mid-district, the sediment environment is belong to marine continental alternation facies with clastic rocks and limestone; In the West Qinling and East Kunlun of the south district, the sediment environment is archipelagic ocean including turbidite rocks of bathyal facies and abyssal facies, basalt, seamount carbonate and so on. During the geological mapping of 1∶250 000 Linxia city and Dingxi City, we found small ocean basin and carbonate seamount formation of early and middle Permian between West Qinling in Ganjia, Xiahe County, Gansu Province. And this can contrast with the archipelagic ocean sediment formation between Qinling and Kunlun in the area of Buqingshan-Huashixia-Xinghai. In late Permian, the sediment is still turbidite rocks of half-sea and deep-sea between Qinling and Qilian, but it is foreland-molasses sediment formation between Qinling and Kunlun.
2007, 32(5): 691-702.
Abstract:
The middle Permian Daguanshan Fm., consisting of reef limestone, is well developed in Xiahe County, Gansu Province and Tongren County, Qinghai Province, China. There exist abundant fossils, such as fibrous sponges, calcisponges, bryozoans, foraminiferas, fusulinidas, calcareous algae and corals. Our research is based on 39 species of foramninfera that belong to 27 generas, which include 16 species of fusulinida pertaining to 11 generas. The foraminifera fauna in this area may be divided into two Non-fusulinida assembldges, two fusulinida assembldges and one fusulinida zone respectively in ascending order as follows: Non-fusulinida assembldges: Pachyphloia-Cribrogenerina-Nodosaria and Cribrogenerina-Hemigordius; two fusulinida assembldges: Parafusulina-Pseudofusuluna assembldge, Cancellina cf. houchangensis Zone Afghanella-Sphaerulina assembldge. We compared the Fusulinida assembldges of Daguanshan Formation with the Fusulinida zones worldwide at the same stratum, and concluded that the age of Daguanshan Formation is Luodian-Lengwu stage, Middle Permian.
The middle Permian Daguanshan Fm., consisting of reef limestone, is well developed in Xiahe County, Gansu Province and Tongren County, Qinghai Province, China. There exist abundant fossils, such as fibrous sponges, calcisponges, bryozoans, foraminiferas, fusulinidas, calcareous algae and corals. Our research is based on 39 species of foramninfera that belong to 27 generas, which include 16 species of fusulinida pertaining to 11 generas. The foraminifera fauna in this area may be divided into two Non-fusulinida assembldges, two fusulinida assembldges and one fusulinida zone respectively in ascending order as follows: Non-fusulinida assembldges: Pachyphloia-Cribrogenerina-Nodosaria and Cribrogenerina-Hemigordius; two fusulinida assembldges: Parafusulina-Pseudofusuluna assembldge, Cancellina cf. houchangensis Zone Afghanella-Sphaerulina assembldge. We compared the Fusulinida assembldges of Daguanshan Formation with the Fusulinida zones worldwide at the same stratum, and concluded that the age of Daguanshan Formation is Luodian-Lengwu stage, Middle Permian.
2007, 32(5): 703-712.
Abstract:
According to the comprehensive analysis of granularity and magnetic susceptibility of late Pleistocene loess-paleosol sequence at Tawan, Lintao County, Gansu Province, the climate change in this area can be divided into seven phases. (1) 1-8.5 m above the bottom (92.4-78.8 kaBP) : the average value of particle diameter and magnetic susceptibility was 24.42 μm and 716.8×10-6 SI, and the annual average temperature and precipitation reached to 7.8 ℃ and 500 mm, being the highest of the seven phases, indicating warm and wet climate. (2) 8.5-14.8 m above the bottom (78.8-65.3 kaBP) : the average value of particle diameter and magnetic susceptibility was 26.83 μm and 442.3×10-6 SI, and the annual average of temperature and precipitation was about 5.2 ℃ and 370 mm. The climate was tepid and dry. (3) 14.8-20.3 m above the bottom (65.3-57.3 kaBP) : the mean of particle diameter and magnetic susceptibility was 25.94 μm and 320.7×10-6 SI, and the annual average temperature and precipitation was about 3.5 ℃ and 280 mm. The climate changed to be mild-dry and slightly cool. (4) 20.3-24.9 m above the bottom (57.3-47.7 kaBP) : the average value of particle diameter and magnetic susceptibility was 25.23 μm and 516.4×10-6SI, and the annual average temperature and precipitation reached 6.0 ℃and 410 mm. It was mild-dry and slightly wet. (5) 24.9-29.4 m above the bottom (47.7-40.9 kaBP) : the mean of particle diameter and susceptibility was 25.46 μm and 299.4×10-6 SI, and the annual average temperature and precipitation was 3.1 ℃ and 270 mm. The climate was mild-dry and slightly cool. (6) 29.4-34.2 m above the bottom (40.9-32.4 kaBP) : the average value of particle diameter and susceptibility was 21.46 μm and 405.5×10-6 SI, and the annual average temperature and precipitation was about 4.7 ℃ and 350 mm. It was mild-dry and slightly wet. (7) 34.2-39 m above the bottom (after 32.4 kaBP) : the average value of particle diameter and susceptibility was 188.89 μm and 381.1×10-6 SI, and the annual average temperature and precipitation was about 4.4 ℃ and 330 mm. The climate was warm and dry. There shows a high comparability between these climate changes in the studied area and the regional environmental evolution. PhaseⅠcorresponds to the warm MIS (marine isotope stage) 5; PhaseⅡandⅢ correspond to the cooling MIS4; Phase Ⅳ, Ⅴand Ⅵ correspond to the warm MIS3; Phase Ⅶ corresponds to the cooling MIS2. Compared with adjacent areas, like Jiuzhoutai in Lanzhou Province and core RM in Zoige, the climate is obvious warmer and wetter in Linxia during the same period.
According to the comprehensive analysis of granularity and magnetic susceptibility of late Pleistocene loess-paleosol sequence at Tawan, Lintao County, Gansu Province, the climate change in this area can be divided into seven phases. (1) 1-8.5 m above the bottom (92.4-78.8 kaBP) : the average value of particle diameter and magnetic susceptibility was 24.42 μm and 716.8×10-6 SI, and the annual average temperature and precipitation reached to 7.8 ℃ and 500 mm, being the highest of the seven phases, indicating warm and wet climate. (2) 8.5-14.8 m above the bottom (78.8-65.3 kaBP) : the average value of particle diameter and magnetic susceptibility was 26.83 μm and 442.3×10-6 SI, and the annual average of temperature and precipitation was about 5.2 ℃ and 370 mm. The climate was tepid and dry. (3) 14.8-20.3 m above the bottom (65.3-57.3 kaBP) : the mean of particle diameter and magnetic susceptibility was 25.94 μm and 320.7×10-6 SI, and the annual average temperature and precipitation was about 3.5 ℃ and 280 mm. The climate changed to be mild-dry and slightly cool. (4) 20.3-24.9 m above the bottom (57.3-47.7 kaBP) : the average value of particle diameter and magnetic susceptibility was 25.23 μm and 516.4×10-6SI, and the annual average temperature and precipitation reached 6.0 ℃and 410 mm. It was mild-dry and slightly wet. (5) 24.9-29.4 m above the bottom (47.7-40.9 kaBP) : the mean of particle diameter and susceptibility was 25.46 μm and 299.4×10-6 SI, and the annual average temperature and precipitation was 3.1 ℃ and 270 mm. The climate was mild-dry and slightly cool. (6) 29.4-34.2 m above the bottom (40.9-32.4 kaBP) : the average value of particle diameter and susceptibility was 21.46 μm and 405.5×10-6 SI, and the annual average temperature and precipitation was about 4.7 ℃ and 350 mm. It was mild-dry and slightly wet. (7) 34.2-39 m above the bottom (after 32.4 kaBP) : the average value of particle diameter and susceptibility was 188.89 μm and 381.1×10-6 SI, and the annual average temperature and precipitation was about 4.4 ℃ and 330 mm. The climate was warm and dry. There shows a high comparability between these climate changes in the studied area and the regional environmental evolution. PhaseⅠcorresponds to the warm MIS (marine isotope stage) 5; PhaseⅡandⅢ correspond to the cooling MIS4; Phase Ⅳ, Ⅴand Ⅵ correspond to the warm MIS3; Phase Ⅶ corresponds to the cooling MIS2. Compared with adjacent areas, like Jiuzhoutai in Lanzhou Province and core RM in Zoige, the climate is obvious warmer and wetter in Linxia during the same period.
2007, 32(5): 713-721.
Abstract:
There are strong, fresh tectonic processes and a series of active faults in the northern part of East Kunlun in Tibetan plateau, controlling the geomorphology and the water system of this area. Most of the active faults have been confirmed, while some are only presumed qualitatively at present. This paper introduces two kinds of geological factors, the Stream Length-gradient index (SL index) and Hack profile, which can effectively reflect regional tectonics, and particularly describes and studies the gradient change of the longitudinal profile of the Kunlun river and the contrast of river terraces in space in Kunlun area. It shows that there exists a corresponding relationship between Hack profile and SL index of the Kunlun river in shape and the mutation of the SL index is mainly controlled by the action of fault. We have also proved the activity of the Kunlunhe-Yeniugou fault and the central fault of east Kunlun from Quaternary, and believe that strong differentia uplift controls the geomorphologic evolution and river development of east Kunlun and will exert far-reaching influence on them.
There are strong, fresh tectonic processes and a series of active faults in the northern part of East Kunlun in Tibetan plateau, controlling the geomorphology and the water system of this area. Most of the active faults have been confirmed, while some are only presumed qualitatively at present. This paper introduces two kinds of geological factors, the Stream Length-gradient index (SL index) and Hack profile, which can effectively reflect regional tectonics, and particularly describes and studies the gradient change of the longitudinal profile of the Kunlun river and the contrast of river terraces in space in Kunlun area. It shows that there exists a corresponding relationship between Hack profile and SL index of the Kunlun river in shape and the mutation of the SL index is mainly controlled by the action of fault. We have also proved the activity of the Kunlunhe-Yeniugou fault and the central fault of east Kunlun from Quaternary, and believe that strong differentia uplift controls the geomorphologic evolution and river development of east Kunlun and will exert far-reaching influence on them.
2007, 32(5): 722-726.
Abstract:
The AB compound type or transitional type fold appears in many sedimentary areas, between thick and thin layers, made by slipping between layers. The fold has more than one hinges, which is the result of uncoaxal superimposed fold, underwent B type fold in early time and A type fold in late time. There is little report about this fold, however it is ubiquitous. In this paper, the author introduced the output state on field of this fold in Tibet, Hubei Wuhan, Sichuan Xichang firstly, then described the geometry shape characters in all trend of this fold, analyzed the deformation control condition of this fold, finally discussed the form and evolvement mechanisms of this fold based on Slump Fold Limit and reference of the form mechanism of sheath fold.
The AB compound type or transitional type fold appears in many sedimentary areas, between thick and thin layers, made by slipping between layers. The fold has more than one hinges, which is the result of uncoaxal superimposed fold, underwent B type fold in early time and A type fold in late time. There is little report about this fold, however it is ubiquitous. In this paper, the author introduced the output state on field of this fold in Tibet, Hubei Wuhan, Sichuan Xichang firstly, then described the geometry shape characters in all trend of this fold, analyzed the deformation control condition of this fold, finally discussed the form and evolvement mechanisms of this fold based on Slump Fold Limit and reference of the form mechanism of sheath fold.
